A test of three hypotheses for latitudinal segregation of the sexes in wintering birds

1981 ◽  
Vol 59 (8) ◽  
pp. 1527-1534 ◽  
Author(s):  
J. P. Myers
Keyword(s):  
Sexual Difference ◽  
Sexual Size Dimorphism ◽  
Bird Species ◽  
Western Hemisphere ◽  
Comparative Data ◽  
Sexual Differences ◽  
Breeding Ground ◽  
Size Dimorphism ◽  
Physiological Tolerance ◽  
Location Data

Three hypotheses have been proposed to explain sexual differences in wintering latitude for different bird species: (1) intersexual behavioral dominance leads the subordinate sex to migrate farther to avoid competition; (2) intrasexual selection favors those individuals of one sex that arrive earlier and thus selects for wintering closer to the breeding ground; and (3) sexual differences in physiological tolerance allow the larger sex to survive harsher climates. Using sex, age, date, and location data from specimens collected south of the breeding range in the western hemisphere, I tested predictions of these hypotheses for two scolopacid shorebirds showing reverse sexual size dimorphism, the red phalarope, Phalaropus fulicarius, and the sanderling, Calidris alba.Neither red phalaropes nor adult sanderlings showed any sexual difference in wintering latitude. First-winter male sanderlings tended to winter farther south than first-winter females. Combined with comparative data from other species of shorebirds and passerines, these results are consistent only with hypothesis 2.

scholarly journals Sexual selection explains Rensch's rule of allometry for sexual size dimorphism

2007 ◽  
Vol 274 (1628) ◽  
pp. 2971-2979 ◽  
Author(s):  
James Dale ◽  
Peter O Dunn ◽  
Jordi Figuerola ◽  
Terje Lislevand ◽  
Tamás Székely ◽  
...  
Keyword(s):  
Sexual Selection ◽  
Sexual Size Dimorphism ◽  
Bird Species ◽  
Confounding Factors ◽  
Allometric Relationship ◽  
Rensch’S Rule ◽  
Size Dimorphism ◽  
Rensch's Rule ◽  
Clear Solution ◽  
General Explanation

In 1950, Rensch first described that in groups of related species, sexual size dimorphism is more pronounced in larger species. This widespread and fundamental allometric relationship is now commonly referred to as ‘Rensch's rule’. However, despite numerous recent studies, we still do not have a general explanation for this allometry. Here we report that patterns of allometry in over 5300 bird species demonstrate that Rensch's rule is driven by a correlated evolutionary change in females to directional sexual selection on males. First, in detailed multivariate analysis, the strength of sexual selection was, by far, the strongest predictor of allometry. This was found to be the case even after controlling for numerous potential confounding factors, such as overall size, degree of ornamentation, phylogenetic history and the range and degree of size dimorphism. Second, in groups where sexual selection is stronger in females, allometry consistently goes in the opposite direction to Rensch's rule. Taken together, these results provide the first clear solution to the long-standing evolutionary problem of allometry for sexual size dimorphism: sexual selection causes size dimorphism to correlate with species size.

scholarly journals Sexual Size Dimorphism and Morphological Evidence Supporting the Recognition of two Subspecies in the Galápagos Dove

The Condor ◽  
2007 ◽  
Vol 109 (1) ◽  
pp. 132-141
Author(s):  
Diego Santiago-Alarcon ◽  
Patricia G. Parker
Keyword(s):  
Body Size ◽  
Sexual Size Dimorphism ◽  
Bird Species ◽  
Morphological Data ◽  
Morphological Evidence ◽  
Life History Variation ◽  
Size Dimorphism ◽  
Selective Pressures ◽  
Trade Offs ◽  
Discriminant Analyses

Abstract Abstract Sexual size dimorphism is a conspicuous trait of many wild bird species. Differences in body size between the sexes might reflect selective pressures and trade-offs to optimize performance. Here, we analyze the size dimorphism of the Galápagos Dove (Zenaida galapagoensis) using principal component and discriminant analyses with samples obtained from six islands: Santiago, Santa Fe, Santa Cruz, Española, Genovesa, and Wolf. We also reanalyze published morphological data but also including additional samples from Wolf Island to account for morphological differences among islands. Males were significantly larger than females. Discriminant analyses correctly classified 98% of males and 100% of females, and cross-validation of the model correctly classified 97% of males and 98% of females. We created two sexual size dimorphism indices using wing chord and tarsus as body-size surrogates. Significant differences were found in the sexual size dimorphism index for both measurements among islands. Significant differences in sexual size dimorphism among islands might indicate the role of different selective pressures acting on individual islands (e.g., competition, predation, resources, sexual selection), which might result in life history variation of the species among islands. For the first time, we provide significant morphological evidence supporting the classification of the Galápagos Dove into two subspecies: Z. g. galapagoensis and Z. g. exsul.

Sexual difference in habitat use of Texas map turtles (Emydidae: Graptemys versa) and its relationship to size dimorphism and diet

2003 ◽  
Vol 81 (7) ◽  
pp. 1185-1191 ◽  
Author(s):  
Peter V Lindeman
Keyword(s):  
Body Size ◽  
Habitat Use ◽  
Sexual Difference ◽  
Young Female ◽  
Sexual Differences ◽  
Adult Males ◽  
Size Dimorphism ◽  
Young Females ◽  
Alternative Hypotheses ◽  
Map Turtles

Sexual differences in habitat use of map turtles (Graptemys spp.) have been attributed to differences in swimming ability as influenced by body size, because females are much larger than males, or to sexual differences in diet. Captures of young female Graptemys versa, which had body sizes similar to those of adult males but diet and trophic morphology more similar to those of larger females, allowed testing of these alternative hypotheses. A variety of single habitat variables measured at the sites of capture performed poorly in separating the three groups of turtles, but multivariate analysis and variables relating to position within the stream produced greater separation, indicating that complex combinations of factors probably influence habitat use. Young females were more similar in their habitat use to large females than to males, and their diet was also more similar to that of larger females, due primarily to the quantities of mollusks consumed. The data supported the hypothesis that habitat separation was the result of dietary rather than body size differences. While dietary differences are probably facilitated by sexual size dimorphism, they may not be the ultimate selective force that produced the size dimorphism.

Growth and sexual size dimorphism in Alberta populations of the eastern short-horned lizard, Phrynosoma douglassi brevirostre

1985 ◽  
Vol 63 (1) ◽  
pp. 139-154 ◽  
Author(s):  
G. Lawrence Powell ◽  
Anthony P. Russell
Keyword(s):  
Growth Model ◽  
Sexual Difference ◽  
Sexual Size Dimorphism ◽  
Growth Models ◽  
Tail Length ◽  
Growth Patterns ◽  
Head Width ◽  
Adult Size ◽  
Adult Males ◽  
Size Dimorphism

Alberta populations of Phrynosoma douglassi brevirostre display marked sexual size dimorphism, adult females being considerably larger than adult males. Discriminant analyses of whole mensural characters and of scaled mensural characters indicate that this dimorphism is present from birth, although it is more strongly expressed after sexual maturity. Recapture data were used to generate modified logistic by weight growth models for snout–vent length (SVL), and allometric models for each sex were generated for growth in tail length, head length, and head width. The SVL growth model for females indicates delayed maturity leading to greater adult size, an expected feature of a female viviparine. The SVL growth model for males indicates that growth ceases sooner than in females, resulting in a smaller adult size. This is possibly a result of male dispersal competition, an hypothesis further borne out by the results of a preliminary analysis of mobility in the two sexes, and may also be influenced by intersexual dietary competition. Differences in head dimensions between the sexes are a function of the differences in SVL at adulthood, but there is a significant sexual difference in the allometric relationship of tail length to SVL. No difference in the growth patterns and adult size of either sex was found to exist over the range in Alberta.

Sexual size dimorphism in relation to age and growth based on skeletochronological analysis in a Tibetan frog

2009 ◽  
Vol 30 (3) ◽  
pp. 351-359 ◽  
Author(s):  
Xin Lu ◽  
Xiaoyan Ma
Keyword(s):  
Growth Rate ◽  
Cross Sections ◽  
Sexual Difference ◽  
Sexual Size Dimorphism ◽  
Population Level ◽  
Age And Growth ◽  
Size Difference ◽  
Size Dimorphism ◽  
Asymptotic Size ◽  
Central Tibet

AbstractThe number of lines of arrested growth (LAGs) in diaphyseal cross-sections of phalanges or femora was used to assess individual age and growth of 612 Nanorana parkeri, including 363 males, 143 females, 70 juveniles, and 36 tadpoles, in a population from central Tibet, China. The oldest immature frogs had an age of 6 years; both the youngest sexually mature males and females were 3 years old. However, the majority of individuals bred for the first time at 5 years in males and 6 years in females. Females had greater average age (6.27 years) and lifespan (11 years) than males (5.72 and 10 years). At the population level, females, on average, were significantly larger in body length (40.3 mm) than males (37.0 mm). However, the significant size difference only occurred when both sexes were over 6 years old, at which most frogs attained maturity. Growth curve and growth rate estimated for each sex based on a von Bertalanffy model showed that females had a larger asymptotic size (54.2 mm) but smaller growth coefficient k (0.16) than males (40.0 mm, 0.37), and that females had greater growth rate than males in all age classes, except at metamorphosis. According to these results, we concluded that the sexual difference of growth between pre- and post-maturation periods contributed to the age-specific sexual size dimorphism of N. parkeri.

Sexual size dimorphism in steppe tortoises (Testudo horsfieldi): growth, maturity, and individual variation

2001 ◽  
Vol 79 (8) ◽  
pp. 1433-1441 ◽  
Author(s):  
Frédéric Lagarde ◽  
Xavier Bonnet ◽  
Brian T Henen ◽  
Johanna Corbin ◽  
Ken A Nagy ◽  
...  
Keyword(s):  
Growth Rate ◽  
Individual Variation ◽  
Sexual Difference ◽  
Sexual Size Dimorphism ◽  
Age And Growth ◽  
Size At Maturity ◽  
Size Dimorphism ◽  
Size Dependent ◽  
Complex Interactions ◽  
Size At Birth

Age and size at maturity are determined through complex interactions among size at birth, growth rate, maturation, and survival. We studied sexual size dimorphism and growth rate and maturation patterns in a long-lived organism, the steppe tortoise (Testudo horsfieldi), using the scute lamina number and width as age and growth measures. There was no sexual difference in the juvenile growth rate, but females matured later and hence were larger at maturity than males. We also observed considerable inter-individual variation in age and size at maturity. In both sexes, precocious animals grew faster during the juvenile phase but matured at a smaller body size than did tardy animals. Consequently, maturity did not seem size-dependent per se but rather was determined by growth rate. The strong variation between and within the sexes in age and size at maturity suggest that different growth trajectories and maturation schedules depend upon sex and individual responses to resource availability.

Effects of food restriction on growth, energy allocation, and sexual size dimorphism in Yarrow’s Spiny Lizard, Sceloporus jarrovii

2008 ◽  
Vol 86 (4) ◽  
pp. 268-276 ◽  
Author(s):  
Robert M. Cox ◽  
Michele M. Barrett ◽  
Henry B. John-Alder
Keyword(s):  
Growth Rate ◽  
Food Restriction ◽  
Sexual Difference ◽  
Sexual Size Dimorphism ◽  
Energy Allocation ◽  
Size Dimorphism ◽  
Available Energy ◽  
Sexually Antagonistic Selection ◽  
Fat Bodies ◽  
Growth Energy

Evolutionary biologists often view sexual size dimorphism (SSD) as a fixed genetic consequence of sexually antagonistic selection, but the actual magnitude of SSD may often be strongly dependent upon proximate environmental factors. Sexual differences in growth rate lead to male-biased SSD in wild populations of Yarrow’s Spiny Lizard ( Sceloporus jarrovii Cope, 1875), yet both sexes grow at similar rates under controlled laboratory conditions. We hypothesized that male-biased SSD in S. jarrovii reflects an obligatory sexual difference in energy allocation to growth versus competing functions, but that an ad libitum diet provides an energy surplus which overwhelms this sex-specific energetic trade-off. To test this hypothesis, we reared juveniles under high (3 crickets/d) and low (1 cricket/d) food availabilities. Food restriction dramatically reduced growth in both sexes but did not differentially affect growth of females relative to males. Food consumption did not differ between sexes, but males grew slightly faster than females at both levels of food availability, indicating a greater fractional allocation of available energy to growth. By contrast, females had larger fat bodies than did males, particularly under food restriction. This sexual difference in energy allocation to storage could explain the slightly higher growth rate of males relative to females.

scholarly journals Limited male incubation ability and the evolution of egg size in shorebirds

2006 ◽  
Vol 2 (2) ◽  
pp. 206-208 ◽  
Author(s):  
Terje Lislevand ◽  
Gavin H Thomas
Keyword(s):  
Body Size ◽  
Egg Size ◽  
Sexual Size Dimorphism ◽  
Bird Species ◽  
Male Body ◽  
Size Dimorphism ◽  
Size Evolution ◽  
Female Body Mass ◽  
Using Data ◽  
The Relationship

In bird species where males incubate but are smaller than females, egg size may be constrained by male body size, and hence ability to incubate the eggs. Using data from 71 such shorebird species, we show that egg size decreases as the degree of female-biased sexual size dimorphism increases, after controlling for female body mass. Relative egg size was not related to mean clutch size. However, when controlling for mating system, the relationship between female-biased sexual size dimorphism and relative egg size was only significant in polyandrous species. The relatively small eggs of socially polyandrous shorebirds have previously been explained as an energy-saving strategy associated with the production of multiple clutches. Our findings suggest that egg size evolution is better explained by male incubation limitation in these birds.

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